In the context of redox reactions, which molecule accepts electrons at the end of the electron transport chain to form water?

• A. ATP
• B. Carbon dioxide (CO2)
• C. Oxygen (O2)
• D. NADH

Answer: (C)

Verified step by step guidance

1. Understand the context of the problem: The electron transport chain is a series of complexes that transfer electrons from electron donors to electron acceptors via redox reactions, and couples this electron transfer with the transfer of protons (H+ ions) across a membrane.
2. Identify the role of oxygen in the electron transport chain: Oxygen acts as the final electron acceptor in the chain. It is essential for the process of oxidative phosphorylation, which occurs in the mitochondria of eukaryotic cells.
3. Recognize the chemical reaction involved: At the end of the electron transport chain, oxygen accepts electrons and combines with protons to form water. The reaction can be represented as: $O_2+4e_{\mathrm{-}}+4H_{\mathrm{+}}\to 2H_{2}O$
4. Clarify why other molecules are not the final electron acceptors: ATP is a product of the electron transport chain, not an electron acceptor. Carbon dioxide (CO2) is a product of cellular respiration but not involved in the electron transport chain. NADH is an electron donor, not an acceptor.
5. Conclude with the importance of oxygen: Oxygen's role as the final electron acceptor is crucial for the production of ATP through oxidative phosphorylation, highlighting its importance in cellular respiration and energy production.